On Wed, Jan 29, 2025 at 03:46:46PM +0100, Richard Biener wrote:
> The following guards the BIT_FIELD_REF expansion fallback for
> MEM_REFs of entities expanded to register (or constant) further,
> avoiding large out-of-bound offsets by, when the access does not
> overlap the base object, expanding the offset as if it were zero.
>
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
>
> I didn't feel lucky enough trying to simply return const0_rtx for
> fully out-of-bound accesses.
>
> OK?
>
> Thanks,
> Richard.
>
> PR middle-end/118692
> * expr.cc (expand_expr_real_1): When expanding a MEM_REF
> as BIT_FIELD_REF avoid large offsets for accesses not
> overlapping the base object.
>
> * gcc.dg/pr118692.c: New testcase.
> ---
> gcc/expr.cc | 8 ++++++++
> gcc/testsuite/gcc.dg/pr118692.c | 10 ++++++++++
> 2 files changed, 18 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/pr118692.c
>
> diff --git a/gcc/expr.cc b/gcc/expr.cc
> index 7f3149b85ee..10467f82c0d 100644
> --- a/gcc/expr.cc
> +++ b/gcc/expr.cc
> @@ -11806,6 +11806,14 @@ expand_expr_real_1 (tree exp, rtx target,
> machine_mode tmode,
> set_mem_size (temp, int_size_in_bytes (type));
> return temp;
> }
> + /* When the access is fully outside of the underlying object
> + expand the offset as zero. This avoids out-of-bound
> + BIT_FIELD_REFs and generates smaller code for these cases
> + with UB. */
> + type_size = tree_to_poly_uint64 (TYPE_SIZE_UNIT (type));
> + if (!ranges_maybe_overlap_p (offset, type_size, 0,
> + GET_MODE_SIZE (DECL_MODE (base))))
> + offset = 0;
> exp = build3 (BIT_FIELD_REF, type, base, TYPE_SIZE (type),
> bitsize_int (offset * BITS_PER_UNIT));
> REF_REVERSE_STORAGE_ORDER (exp) = reverse;
> diff --git a/gcc/testsuite/gcc.dg/pr118692.c b/gcc/testsuite/gcc.dg/pr118692.c
> new file mode 100644
> index 00000000000..49cff35b8b7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr118692.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +_Complex cf;
Please use _Complex double here.
> +
> +void
> +foo(char c)
> +{
> + cf += *(_Complex *)__builtin_memcpy(8143523003042804629 + &c, 0, 0);
Ditto here.
I think it might be a good idea to use LL suffix after the constant too.
Otherwise LGTM.
Jakub
